The invention relates to a method for measuring the thickness of a coating on a component section of a rotating component during a coating process, a device for conducting a method of this type, a method for producing a component as well as a coating system.
The application of sprayed layers is associated with specific uncertainties and irregularities due to the jet spray of particles that can be influenced only in a limited way, so that reproducibility with respect to layer distribution and dimensional accuracy is very limited or is feasible only with correspondingly high tolerances. Therefore, in order to obtain a required coating thickness, an abrading post-processing such as a grinding or sanding is frequently necessary.
In the meantime, 3D-measurement systems for aligning the spray nozzle prior to each spray process are known, by means of which the reproducibility of the layer distribution is clearly increased and by means of which corrective measures are possible with respect to the spray angle, which, in conjunction with the component geometry, decisively determines the uniformity of layer application. The prerequisite for optimal alignment and control of the spray nozzle, however, is the regular inspection of each layer with respect to its thickness during the coating process and thus in real time.
A known measurement method for measuring layer thicknesses and a known measurement device are shown in DE 10 2005 009 262 A1. A sensor detects its distance from the component surface and a sensor detects its distance from the layer surface. The actual layer thickness is then measured from the difference between the two distance values.
In the German Patent Application DE 10 2006 052 587 A1 of the Applicant, a measurement method and a measurement device having three sensors is presented, which is based on a principle similar to the method or the device according to the above-named DE 10 2005 009 262 A1. In this case, the third sensor monitors the position of one of the two sensors relative to the component and detects the position of the component at specific time points. This makes possible certain information of which region the monitored sensor is measuring, so that the layer distribution can be precisely determined.
A method and a device for measuring the layer thickness of a rotating component having only one optical sensor are presented in WO 2006/116841 A1. The component rotates around its longitudinal axis and is coated via a spray nozzle traveling along the longitudinal axis, whereby the layer is applied in a spiraling strip. For detecting the layer thickness, a camera is provided, which detects the movement of a laser beam scanning the surface of the coating, so that the layer thickness can be determined basically via the step formation in the edge region between two strips.
A measurement method and a measurement device for measuring the layer thickness of a rotating component having only one optical sensor are also known from U.S. Pat. No. 6,832,577 B2. At the beginning of the coating process, a required quantity of powder is determined. The component is then positioned in a field by parallel laser beams lying in a plane. During coating, a beam shadow imaging the outer contour of the component is formed, and the width of this shadow increases with increasing layer thickness. The component is also detected optically by the optical sensor and a plurality of single images of the changing outer contour are prepared. After spraying a specific quantity of powder, the coating process is interrupted and the layer application is evaluated taking into consideration the quantity of powder sprayed, the beam shadow and the single images.
It is problematical, however, that a heat expansion of the component during the coating is not considered. For a precise determination of layer thickness, however, exact knowledge of the component core temperature is essential, since a radial heat expansion of the component frequently is found of the same order of magnitude as a common targeted layer thickness. In fact, it is known from US 2009/0061075 A1 to monitor the temperature by means of a pyrometer directed on the coating, but this temperature only records the surface temperature of the last layer produced. This problem is intensified if the component is cooled on the side of the outer periphery during the coating process.